The effects of season, age, sex and dietary Cr supplementation on some serum biochemical markers were investigated in broilers. A total of 600 Ross-PM3 one day old broiler chicks (300 in winter and 300 in summer) were used. In each experimental period, 150 male and 150 female chicks were divided into two groups according to dietary CrCl3 supplementation (0 ppm in control, 20 ppm CrCl3. 6H(2)O in treated group). Blood samples were collected on the 1(st), 3(rd) and 6(th) weeks of age and the serum AST, CK activities and inorganic phosphorus (iP), K, total protein, albumin, globulin, and Cr concentrations and body weight were determined. Season greatly influenced all analysed markers (p<0.01) except serum K concentrations. Significant differences between male and female chicks were observed for serum AST activity (p<0.001), globulin concentration (p<0.05) and body weight (p<0.001). All markers were significantly changed with aging (p<0.001). Dietary Cr supplementation significantly increased AST and CK activities (p<0.05), mineral concentrations (p<0.001) and body weight (p<0.001). In conclusion, although season, age, sex and Cr treatment affected blood markers, they stayed within normal ranges. Besides, because improvement of body weight gain, dietary Cr supplementation (20 ppm) may be economically beneficial in broilers.